Validity of Coronary Artery Calcium Score in Cardiovascular Risk Assessment
Coronary artery calcium (CAC) scoring is a highly valid and robust tool for cardiovascular risk assessment, providing superior predictive value compared to traditional risk factor assessments alone, particularly for intermediate-risk patients. 1
Predictive Value and Risk Stratification
CAC scoring directly quantifies coronary atherosclerosis burden and serves as a reliable marker of vascular age and subclinical atherosclerosis. It is consistently the single best predictor of atherosclerotic cardiovascular disease (ASCVD) risk when compared with other nontraditional markers such as carotid intimal thickness, ankle-brachial index, and C-reactive protein 1.
The risk of adverse cardiovascular events increases proportionally with the CAC score:
- CAC = 0: Low risk, annual mortality rate <0.5%, coronary event rate 0.4% over 3-5 years 1
- CAC = 1-99: Mild to moderate risk, 1.2-2.2 times higher risk of cardiovascular events 1
- CAC = 100-399: Moderate to high risk, 4.3 times higher relative risk 1
- CAC = 400 or higher: Severe to very high risk, 7.2 times higher relative risk 1
- CAC = 1000 or higher: Extremely high risk, 10.8 times higher relative risk 1
A meta-analysis demonstrated that patients with CAC > 0 had a significantly increased risk of major adverse cardiovascular and cerebrovascular events (MACE) compared to those with CAC = 0 (pooled risk ratio 4.05) in asymptomatic individuals and even higher (pooled risk ratio 6.06) in symptomatic individuals 2.
Clinical Applications and Guidelines
The American College of Cardiology/American Heart Association (2019) recommends CAC scoring for:
- Adults 40-75 years with intermediate ASCVD risk
- Selected adults with borderline risk when decisions about preventive interventions are uncertain 1
The Society of Cardiovascular Computed Tomography (2017) recommends CAC scoring for:
- Asymptomatic adults 40-75 years with borderline to intermediate risk
- Selected low-risk adults with family history of premature CAD 1
Distribution and Location of CAC
The distribution of CAC provides additional prognostic information beyond the total score:
- Left main coronary artery (LMCA) calcification carries particularly high risk
- Annual risk-adjusted mortality was 1.73% for LMCA CACS = 101–399 and 7.71% for LMCA CACS > 400 3
- Mortality risk was 20% higher if <25% of the CAC was in the LMCA and 40% higher when >25% was in the LMCA, versus no LMCA calcification 3
- The more vessels with CAC (including 2-vessel, 3-vessel and 3-vessel + LMCA disease), the higher the all-cause mortality 3
Management Recommendations Based on CAC
CAC scoring should guide clinical management decisions:
- CAC = 0: May allow "de-risking" of patients and potential deferral of statin therapy in intermediate-risk individuals 1
- CAC = 1-99: Consider lifestyle modifications; pharmacotherapy generally not recommended 4
- CAC = 100-399: Consider moderate-intensity statin therapy if above 75th percentile for age/sex 1, 4
- CAC ≥ 400: High-intensity statin therapy recommended to reduce LDL-C by ≥50%, consider adding ezetimibe if LDL-C goals not achieved 1, 4
Follow-up and Monitoring
Recommended follow-up intervals for CAC testing:
- CAC = 0: Repeat in 5-7 years
- CAC = 1-99: Repeat in 3-5 years
- CAC ≥ 100 or diabetes: Repeat in 3 years 1
Limitations and Pitfalls
Important limitations to consider:
- CAC=0 does not completely exclude obstructive coronary artery disease, as noncontrast CT does not detect noncalcified atherosclerotic plaque 1
- CAC represents only about 20% of the total atherosclerosis burden, as not all plaques contain calcium 1
- In certain metabolic conditions (diabetes, uremia, disorders of calcium-phosphate homeostasis), medial calcification may occur instead of the intimal calcification seen in coronary atherosclerosis 3
Safety Considerations
The radiation dose for CAC scoring is relatively small (0.37 ± 0.16 mSv), which is slightly lower than screening mammography (0.44-0.56 mSv) 1, making it a safe diagnostic tool with minimal radiation exposure.